Just as there are marked differences in the structure and composition of hard and soft contact lenses, there are also marked differences in the maintenance and care or treatment of the various types of hard, semi-hard and soft lenses. While patient care and treatment of hard contact or conventional contact lenses is relatively simple and uncomplicated, the proper care and treatment of the newer soft and hydrophilic lenses has proved to be more complex and time consuming.
The primary difference between the conventional hard contact lens and the more complex soft lenses is the marked increase in the polar or water attracting centers of the hydrophilic gel material. It is this property of the hydrophilic gel lens that gives the soft lens its own unique physical properties and clinical behaviour. This polar or water attracting center of the gel material is represented in the hydroxyethyl methacrylate bond as a hydroxyl group (--OH) which attracts and holds large amounts of water. It is this high water content held in the expanded matrix of the hydrophilic gel lens which leads to the special difficulties in and disinfecting or asepticising the soft hydrophilic lens. The hydrophilic nature of soft contact lenses makes the lenses vulnerable to bacterial contamination. While studies have domonstrated that bacteria cannot penetrate the actual intramolecular pores of the hydrophilic lens, except in defective lenses, the bacteria have an affinity for the protein and tear deposits on the surfaces of the lens matrix. In particular, the tears and fluids absorbed by the soft lenses serve as excellent bacterial culture media. If defects or nicks occur in the lens either during manufacture or subsequent patient wear, bacteria may find a haven to grow and be sheltered from superficial lens cleaning and disinfection.
Potentially harmful fungi also prove a possible danger to the soft contact lens. Fungi, like bacteria, can thrive in tear secretions or deposits and penetrate the lens material directly if enzymatic degradation of the lens material has taken place.
Other problems can accrue from incorrect and careless handling of the soft lenses by the patient himself. Many potential contaminants and lens deposits can be transferred from unwashed fingers to the surface of the soft lens. These include oily deposits from the skin, sweat, skin lotions and creams, mascara, detergents, lipstick and even nicotine. Controlled studies have demonstrated that bacterial contaminants occur in 43% of the makeup used by women, and fungal contaminants in 12%. Attempts to effect sterilization of the lenses by boiling, for example, can be cumbersome in addition to causing permanent damage to the lenses if done improperly. If the patient has used impure water for storage and rinsing of the lenses, undesirable deposits such as calcium, iron and insoluble divalent and trivalent metallic salts as well as other chemical deposits can collect on the lens surfaces.
Therefore, a need has arisen for an effective composition to counteract and mitigate the above described effects of improper hygiene and lens handling as well as to provide optimum disinfection and storage of the soft lens between lens wearing periods. In addition, the active ingredients of an effective contact lens solution should preferably: (1) disinfect clean soft lenses within a period of four to six hours and produce D values of a 90% kill rate of microorganisms, selected fungal and yeast organisms, and viral agents such as herpes simplex; (2) not be easily inactivated by small amounts of proteins, lipids or other tear and extraneous components and deposits; (3) not bind to protein or other lens surface deposits from the eye; and (4) not react with or absorb to the soft lens material or matrix. For example, several antiseptic agents which meet the above requirement for rapid and effective kill of a broad range of microorganisms have proved to be unsuitable for use in soft lens treatment solutions, in that these agents are incompatible with the soft lens material or bind with protein deposits on the surfaces of the lens matrix. Other antiseptic agents are unacceptable for use in soft lens solutions since they are concentrated by the lens material, to the extent that they cause discomfort and potential damage to the corneal surface of the wearer's eyes. Benzalkonium chloride is one such antiseptic agent which meets the requirements for effective and rapid killing of microorganisms but is unacceptable because it binds with many types of soft lens material and also binds with protein deposits on the lens surface.
One type of cold disinfecting solution for soft contact lenses uses chlorohexidine. However, chlorohexidine is absorbed by the soft contact lens material and gradually eluded into the eye often causing excessive burning, irritation and red eye, which can prevent the patient from wearing the lenses.
Therefore, a need has arisen for a highly effective cold storage and disinfecting solution for the overnight or interim disinfection and storage of soft and semi-hard contact lenses which meet the aforesaid requirements.